Process and product for protecting aluminium, magnesium and their alloys against corrosion



Patented June 23, 1931 UNITED STATES PATENT OFFICE cILARLEs OULANGERQOFCLICHY, FRANCE, ASSIGNOR T0 soomrn con'rm'nm'nnn PARKER, 01 CLICHY,FRANCE PROCESS .AN'DIPRODUGT FOR PROTECTING ALU MINIUM, MAGNESIUM ANDTHEIR. Ad)- I LOYS AGAINST CORROSION No Drawing. Application filedOctober 21, 1929, Serial No. 401,384, and in Fra'nce November 10, 1928.

The present inventionhas for itsobject a process of protecting thesurface of aluminium, magnesium, or their alloys, against attacks bysalt solutions,- such as chloride of sodium, or by moist air loaded withparticles of these solutions, for instance sea air capable of causingthe alteration or corrosion of the metal. p The. process is essentiallycharacterized by the fact that, by"means of a salt bath, a protectingdeposit is formed at the surface of the metal, and that, to form thisdeposit, use

as chromates, vanadates, molybda-tes, tungstates, ititanates, uranates,niobates, manganates, etc., either alone, or mixed together.

' It is necessary that the metal chosen can I give at least twooxidesthe most oxygenated of which gives an alkalisalt soluble in analkaline solution. By reduction, the corresponding oxide is brought backto the state of sub-oxide. Thus, a manganate corresponding to managanic"acid MnO H O, will be brought back to the state of'Mn Q or of Mn O whichare stable, do not corrode when inuse, and form at the surface ofaluminium, for instance, the. desired protecting layer.

The formation of this layer can be obtained by immersion of the metalpart or member in a bath ofthe chosen salt, at a suitable degree ofconcentration and at a suitable temperature. 'The bath must be renderedalkaline by the'addition of an alkali'car.

bonate, droxide. For instance for protecting an article made ofaluminium, it can be immersed in a boiling solution of carbonate ofsodium at about 1%, and of molybdate of sodium or potassium It has beenfound that the following ess, derived from the preceding one, .procuresspecial advantages concerning the practical industrial carrying'out ofthe process.

better preservation of-these salts in presence of moisture can beobtained by addition of a small quantity of a salt, such as borate' ofsoda, which is without action on the deposited oxide film be protected.1

is made of solutions of alkali metal salts such-1 or oi? thecorresponding alkali hyand on the metal to A mixture of these two saltsgives, in

sti'tute an example, since use can be made of sulphoitun state insteadof sulpho-molybdate, or o sulpho-uranate, with phosphovanadate orphospho-manganate, either alone or mixed together.

' By way of example, the following proportions can be indicated forprotecting aluminium:

Mixture of'phospho-chromate and of sulpho-molybdate of potash0.5% of thebath.

Carbonate of Solvay soda: 1% of the solution. 1

The concentration of the solution in alkali carbonate varies butslightly inuse. The

loss of salt caused by deposition, will be compensated by theintroduction of a; further quantity of salt in become weaker.

The above mentioned proportion as the bath will salts are stable, theydo not alter under the action of air and moisture, they are extremelysoluble. The mixing of these salts with carbonate of soda pro cures thesame qualities of unalterableness and of solubility.

The treatment of the article to beprotected is efi'ected at boilingpoint; the duration of the treatment depends on the thickness of thedeposit it is desired to obtain.

.' The protecting layer constitutes an excellent holding surface for anyvarnish, paint,

"fatty bodies, enamels, etc.

Claims 1. Process for protecting articles made of aluminium, magnesium,or their alloys, against corrosion, of the said articles in a bathcontaining carbonate of soda and an alkali salt of the most oxygenatedoxide of a metal capable of forming at least two oxides themostoxygenated' one being soluble .in alkaline solution and the lessoxygenated one being insoluble.

2. Process for protecting articles made of 1M comprising the treatmentaluminium, magnesium, or their alloys, against corrosion, comprising thetreatment of the said articles in a bath containing carbonate of sodaand a mixture of alkali sul- 5 pho-molybdate and alkali phosphochromatei 3. Process for protecting articles "made of aluminium,magnesium, or their alloys, against corrosion, comprising the treatment0 the said'articles in a bath containing carbonate of soda and a mixturecomposed of 1 part of alkali sulpho-molybdate and 5 parts of alkaliphospho-chromate. r 4. Product servin to reduce a protecting layer onarticles 111 e o aluminium, magnesium or their alloys, comprising acarbonate of alkali metal and a salt formed by an alkali metal and byone of the following metals; I vanadium, molybdenum, tungsten, titanium,

uranium, niobium, manganese and chromium.

5. .Process for protecting articles made of aluminium, magnesium, ortheir alloys, comprising the treatmentof the said articles in. a

. ,ath, containing carbonate of soda and an alkali salt of, a metalcapable of givin atleast two oxides, such as vanadium, moly denum,tungsten, titanium, uranium, niobium, manganese and chromium.

In testimony whereof I have hereunto so aflixed my signature.

CHARLES BOULANGER.

